University of Hertfordshire

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From the same journal

By the same authors

A Gamma-Ray Flare in NRAO 190

Research output: Contribution to journalArticle

  • T. A. McGlynn
  • R. C. Hartman
  • S. D. Bloom
  • M. Aller
  • H. Aller
  • A. V. Filippenko
  • A. J. Barth
  • W. K. Gear
  • A. P. Marscher
  • J. R. Mattox
  • W. Reich
  • E. I. Robson
  • J. Schramm
  • Jason Stevens
  • H. Teraesranta
  • M. Tornikoski
  • W. T. Vestrand
  • S. Wagner
  • A. Heines
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Original languageEnglish
Pages (from-to)625-
JournalThe Astrophysical Journal
Journal publication date1 May 1997
Publication statusPublished - 1 May 1997


We describe observations of the quasi-stellar object (QSO) NRAO 190 during a gamma-ray flare from 1994 August 9 to 1994 August 29. This QSO was serendipitously detected by the EGRET instrument on the Compton Gamma Ray Observatory in a gamma-ray flare with a luminosity at least 10 times that of its quiescent state. Optical, radio, and microwave data were obtained during or near the gamma-ray observations.

The historical behavior of this object places it in the category of bright, flat-spectrum radio sources with strong optical variability that appear to form the largest class of non-Galactic high-energy gamma-ray sources. During the gamma-ray flare the source is observed with l(E > 100 MeV) = 8.4 ± 1.2 × 10-7 photons s-1 cm-2. A single power-law model gives a best-fit photon index of γ = -1.83 ± 0.14.

Little evidence for major radio variability is seen during the flare or immediately afterward, although there is some increase in the 10-100 GHz flux over the next several months. There may be a slight hardening of the radio spectrum. In the optical region there are significant fluctuations on timescales of 1 day or less, although the overall optical luminosity is within the range of previous measurements. Optical observations a few weeks after the gamma-ray observations show a drop of about 60% and reduced variability. A contemporary optical spectrum shows that the source may be slightly harder than seen in a previously published spectrum. Radio monitoring of the source over the year subsequent to the flare has shown a very substantial drop in the flux at many frequencies.


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